In the production of cardboard, two or more paper webs, at least one of which is corrugated in the course of the production process, are glued together. To that end, the individual paper webs to be processed and the finished cardboard as well must be transported at a predetermined speed through or inside the cardboard making system, which comprises a plurality of machines or processing stations disposed one after the other.
For transporting the webs, either separate feeding devices, so-called pull-off devices, which pull the affected web of material through one or more upstream processing stations or machines, or feeding devices that are integrated into an individual machine or processing station and that pull the web of material through the applicable machine or processing station and optionally also through one or more upstream machines or processing stations are used. Slip between the driving or pulling elements and the web of material must be avoided if at all possible, so that a constant feeding speed is assured, to avoid impairment of the web of material to be fed.
It is known, for instance from Published, Non-Examined German Patent Application DE-OS 22 01 742 to pull the web of cardboard through an upstream drying apparatus by means of a separate feeding device, which comprises endless upper and lower belts.
DE-OS 22 01 742 also discloses an integrated drying and transporting apparatus, in which the transport of the fully glued-together cardboard inside the drying and transporting apparatus is transported by means of one endless upper and one lower belt, and the drying of the web of cardboard is effected by suction of an air stream through the interior of the cardboard, crosswise to the travel direction of the web of cardboard. Because of the resultant negative pressure in the interior of the cardboard, high frictional adhesion also results between the cardboard to be transported and the upper or lower belt. As a result, it is attained that there is only slight play between the belts and the respective surfaces of the web of cardboard.
However, this method for avoiding undesirably high slip between the cardboard to be transported and the endless belt is restricted to this special drying apparatus. In particular, this method cannot be employed in a transporting apparatus for a smooth paper web.
From German Patent Disclosure DE 42 12 847 A1, a heating device for a cardboard-making system with an integrated feeding apparatus is also known, in which the heater comprises heating places by way of which the web of cardboard that is to be dried is fed by means of an endless belt. Above the lower run of the endless belt, which is the run that feeds the web of cardboard, one or more contact-pressure devices are arranged, which pressure the lower run of the endless belt against the top of the web of cardboard. These contact-pressure devices may for instance be embodied as pressure rollers or pressure hoods that can be raised and lowered. The amount of pressure for pressing the run of the endless belt against the top of the web of cardboard, must be dimensioned such that the frictional adhesion of the endless belt relative to the web of cardboard is always greater than the sliding friction between the web of cardboard and the heating surface or surfaces.
For controlling the quantity of heat transferred to the web of cardboard, it is known from DE 42 12 847 A1 to measure the temperature or moisture content of the arriving web of cardboard or the departing web of cardboard and to control the pressure values of the contact-pressure device as a function of the measured temperature or moisture values. A disadvantage of all these known apparatuses, however, is that slip between the web of material to be fed and the elements that feed the web of material cannot be avoided in every situation. Especially when there are changes in process parameters (such as temperature, travel speed of the web of material, etc.), changes in parameters of the web of material (such as width, thickness, surface property, etc.), or during the startup and shutdown phase of the machine, or in other words under positive or negative acceleration, it is impossible with adequate certainty to avoid slip in the known feeding apparatuses. Especially when the cardboard-making system is converted to produce other web widths, different types of cardboard, or for processing different qualities of starting materials, currently no resetting of the transport apparatuses is performed.